Balloon expandable cement director and related methods

ABSTRACT

The invention relates to a cement director for insertion within a vertebral body or other body structure, and related methods of use. An example method includes creating a cavity in a vertebral body, inserting a collapsible mesh structure into the cavity in a collapsed state, wherein the collapsible mesh structure comprises regions of different permeability to a bone cement, inflating a balloon within the collapsible mesh structure to expand the mesh structure, and injecting a bone cement into the mesh structure, wherein the bone cement flows preferentially out of the mesh structure through at least one region of greater permeability.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/035,423, filed Feb. 25, 2011, which claims priority to U.S.provisional patent application No. 61/308,055, filed Feb. 25, 2010, thedisclosures of which are hereby incorporated herein by reference intheir entireties for all purposes. This application is also related toU.S. Pat. No. 7,465,310, issued Dec. 16, 2008, U.S. patent applicationSer. No. 12/241,979, filed Sep. 30, 2008, U.S. patent application Ser.No. 11/957,022, filed Dec. 14, 2007, U.S. patent application Ser. No.11/957,039, filed Dec. 14, 2007, U.S. patent application Ser. No.12/486,439, filed Jun. 17, 2009, and U.S. provisional patent applicationNo. 61/210,771, filed Mar. 23, 2009, the disclosures of all of which arebeing incorporate herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates generally to the field of orthopedicdevices, and more particularly to systems and related methods forinjection of bone cement into vertebral bodies to facilitate treatmentof a vertebral compression fracture.

BACKGROUND OF THE INVENTION

There are many disease states that cause bone defects in the spinalcolumn. For instance, osteoporosis and other metabolic bone conditionsweaken the bone structure and predispose the bone to fracture. If nottreated, certain fractures and bone defects of the vertebral body mayproduce intolerable pain, and may lead to the development of deformityand severe medical complications.

Bone weakening may also result from benign or malignant lesions of thespinal column. Tumors often compromise the structural integrity of thebone and thus require surgical stabilization and repair of defects withbiocompatible materials such as bone grafts or cements. Bone tumors ofthe spine are relatively common, and many cause vertebral compressionfracture.

More than 700,000 osteoporotic compression fractures of the vertebraeoccur each year in the United States—primarily in the elderly femalepopulation. Until recently, treatment of such fractures was limited toconservative, non-operative therapies such as bed rest, bracing, andmedications.

One surgical technique for treating a vertebral compression fracture,including injecting or filling the fracture bone or bone defect withbiocompatible bone cement, is called “vertebroplasty.” This techniquewas developed in the mid 1980's to address the inadequacy ofconservative treatment for vertebral body fracture. This procedureinvolves injecting radio-opaque bone cement directly into a fracturevoid, through a minimally invasive cannula or needle, under fluoroscopiccontrol. The cement is pressurized by a syringe or similar plungermechanism, thus causing the cement to fill the void and penetrate theinterstices of a broken trabecular bone. Once cured, the cementstabilizes the fracture and eliminates or reduces pain. Bone cements aregenerally formulations of non-resorbable biocompatible polymers such asPMMA (polymethylmethacrylate), or resorbable calcium phosphate cementswhich allow for the gradual replacement of the cement with living bone.Both types of bone cements have been used successfully in the treatmentof bone defects secondary to compression fractures of the vertebralbody.

One clinical issue associated with vertebroplasty is containment of thecement within the margins of the defect. For instance, an osteoporoticcompression fracture usually compromises portions of the cortical bonecreating pathways to cement leakage. Thus, there is a risk of cementflowing beyond the confines of the bone into the body cavity. Cementleakage into the spinal canal, for instance, can have grave consequencesto the patient.

Yet another significant risk associated with vertebroplasty is theinjection of cement directly into the venous system, since the veinswithin the vertebral body are larger than the tip of the needle used toinject the cement. A combination of injection pressure and inherentvascular pressure may cause unintended uptake of cement into thepulmonary vessel system, with potentially disastrous consequencesincluding embolism to the lungs.

One technique which has gained popularity in recent years is a modifiedvertebroplasty technique in which a “balloon tamp” is inserted into thevertebral body via a cannula approach to expand or distract thefractured bone and create a void within the cancellous structure.Balloon tamps are inflated using pressurized fluid such as salinesolution. The inflation of a balloon membrane produces radial forces onthe surface of the membrane and forms a cavity in the bone. Whendeflated and removed, the membrane leaves a cavity that is subsequentlyfilled with bone cement. The formation of a cavity within the boneallows for the injection of more viscous cement material, which may berelatively less prone to leakage.

In certain instances, such as the treatment of acute or mobilefractures, the balloon is also effective at “reducing” the fracture andrestoring anatomic shape to a fractured body. In particular, balloondilatation in bone is maximally effective if the balloon device istargeted inferior to, or below, the fracture plane. In this instance,the balloon dilatation may distract, or lift, a fracture bone fragment,such as the vertebral body endplate.

In other instances, such as chronic or partially healed fractures,balloons are less effective at “reducing” the fracture because radialforces are insufficient. Often the bone in an incompletely healingfracture is too dense and strong, and requires more aggressive cuttingtreatment, such as a drill or reamer tool to create a sufficient cavity.In these more challenging cases, injecting bone cement into a cavitycreated by a balloon or a reamer in the vicinity of the fracture is notalways sufficient to stabilize the bone and relieve pain, even in theabsence of fracture reduction. While fracture reduction may bedesirable, prior methods of implementing fracture reduction using aballoon have generally been ineffective.

SUMMARY OF THE INVENTION

The present invention is directed towards novel methods and devices fordirecting bone cement into a vertebral body. The methods and devicesdisclosed herein may include a cement director and, for example, an atleast partially balloon expandable cement director, for insertion into avertebral body to assist in controlling the injection of bone cementused, for example, to stabilize vertebral compression fractures.

One aspect of the invention relates to a method of treating a vertebralbody including the steps of creating a cavity in a vertebral body,inserting a collapsible mesh structure into the cavity in a collapsedstate, wherein the collapsible mesh structure includes regions ofdifferent permeability to a bone cement, inflating a balloon within thecollapsible mesh structure to expand the mesh structure, and injecting abone cement into the mesh structure, wherein the bone cement flowspreferentially out of the mesh structure through at least one region ofgreater permeability.

In one embodiment, the mesh structure includes a plurality of layers.The mesh structure may include a first layer including, or consistingessentially of, a first shape memory material in an austenite phase atbody temperature (e.g., approximately 100° F.), a second layerincluding, or consisting essentially of, a second shape memory materialin a martensite phase at body temperature and, optionally, a coveringlayer. In one embodiment, the mesh structure includes a shape memorymaterial such as, but not limited to, nickel titanium (Ni—Ti). The shapememory material may be formed in an austenite phase at body temperature.

In one embodiment the surface of the mesh structure is covered by acovering layer. The covering layer may be impermeable, or substantiallyimpermeable, to the bone cement. The covering layer may include anelastic material. The elastic material may include, or consistessentially of, silicone, polyurethane, styrene, isobutylene, polyester,nylon, natural fiber material, and/or combinations thereof. In oneembodiment, the covering layer covers at least one of an interiorsurface and an exterior surface of the mesh structure. The at least oneregion of greater permeability may include, or consist essentially of,one or more regions that are not covered by the covering layer. In oneembodiment, the covering layer includes a textile such as, but notlimited to, a knitted fabric, a braided fabric, and/or a woven fabric.

In one embodiment, the at least one region of greater permeabilityincludes, or consists essentially of, at least one hole in a wall of themesh structure. In one embodiment, the collapsible mesh structure is atleast partially self-expandable from its collapsed state. The balloonmay be inserted into the interior of the mesh structure prior to themesh structure being inserted into the cavity. One embodiment of themethod further includes deflating the inflated balloon, wherein the meshstructure maintains an expanded form upon deflation of the balloon, andremoving the deflated balloon from the collapsible mesh structure. Theballoon may be inflated with sufficient pressure to move endplates ofthe vertebral body apart. The mesh structure may be expanded to about aboundary of the cavity.

Another aspect of the invention includes a collapsible device forinsertion into a cavity in a vertebral body. The collapsible deviceincludes at least one boundary wall having a closed distal end and anopen proximal end adapted to releasably couple to a deployment device.The boundary wall includes a mesh structure having a first layerincluding, or consisting essentially of, a first shape memory materialin an austenite phase at body temperature, a second layer including, orconsisting essentially of, a second shape memory material in amartensite phase at body temperature, a cover layer, and at least oneregion of different permeability to a bone cement.

One or both of the shape memory materials may include, or consistessentially of, nickel titanium. The covering layer may cover thesurface of the mesh structure and may be impermeable to bone cement. Inone embodiment, the covering layer includes, or consists essentially of,an elastic material. The elastic material may include, or consistessentially of, silicone, polyurethane, styrene, isobutylene, polyester,nylon, natural fiber material, and/or combinations thereof. The coveringlayer may cover at least one of an interior surface and an exteriorsurface of the mesh structure. The at least one region of greaterpermeability may include, or consist essentially of, one or more regionsthat are not covered by the covering layer.

The covering layer may include, or consist essentially of, a textilesuch as, but not limited to, a knitted fabric, a braided fabric and/or awoven fabric. The at least one region of greater permeability mayinclude, or consist essentially of, at least one hole in one or morelayers of the mesh structure. The collapsible mesh structure may be atleast partially self-expandable.

Yet another aspect of the invention includes a system for deploying acollapsible device into a cavity formed in a vertebral body. The systemmay include a delivery device including a distal end for insertion intoa vertebral body and a proximal end including a handle, means forreleasably coupling a collapsible implant to the distal end of thedelivery device, and a balloon coupled at the distal end of the deliverydevice and adapted to expand the collapsible implant when disposedtherein. The collapsible implant may include a first layer including, orconsisting essentially of, a first shape memory material formed in anaustenite phase, a second layer including, or consisting essentially of,a second shape memory material formed in a martensite phase, a coverlayer, and one or more regions of different permeability to a bonecement.

In one embodiment, the system may include a push rod adapted to beremovably insertable through the delivery device and into the implant tohold the implant in a collapsed configuration prior to deployment. Inone embodiment, the system may include a sheath adapted to removablyextend through the delivery device and over the implant to hold theimplant in a collapsed configuration prior to deployment.

Yet another aspect of the invention includes an expandable device forinsertion into a cavity in a vertebral body. The device includes atleast one mesh structure including, or consisting essentially of, afirst shape memory material in a martensite phase at body temperature.The mesh structure includes a closed distal end, an open proximal endadapted to releasably couple to a deployment device, and at least oneregion of different permeability to a bone cement. The mesh structure isexpandable from an unexpanded configuration to an expanded configurationby expansion of a balloon within an interior of the mesh structure, andthe mesh structure is adapted to maintain the expanded configurationafter removal of the balloon from the interior of the mesh structure.

In one embodiment, the shape memory material includes, or consistsessentially of, nickel titanium. The mesh structure may also include asecond layer including, or consisting essentially of, a second shapememory material in an austenite phase at body temperature.

In one embodiment, the mesh structure may further include a coveringlayer. The covering layer may be impermeable to bone cement. Thecovering layer may include, or consist essentially of, an elasticmaterial. The elastic material may be selected from materials such as,but not limited to, silicone, polyurethane, styrene, isobutylene,polyester, nylon, natural fiber material, and/or combinations thereof.The covering layer may cover at least one of an interior surface and anexterior surface of the mesh structure. The covering layer may include,or consist essentially of, a textile selected from the group consistingof a knitted fabric, a braided fabric, and/or a woven fabric. In oneembodiment, at least one region of greater permeability comprises aregion that is not covered by the covering layer. In one embodiment, theat least one region of greater permeability may include, or consistessentially of, at least one hole in one or more layers of the meshstructure.

In one embodiment, the mesh structure is expandable only by expansion ofan expansion element, such as, but not limited to, a balloon. In analternative embodiment, the mesh structure is at least partiallyself-expandable.

Yet another aspect of the invention includes a system for deploying anexpandable device into a cavity formed in a vertebral body. The systemincludes a delivery device including a distal end for insertion into avertebral body and a proximal end including a handle, means forreleasably coupling an expandable device to the distal end of thedelivery device, and a balloon coupled at the distal end of the deliverydevice and adapted to expand the collapsible implant when disposedtherein. The expandable device may include a shape memory material in amartensite phase at body temperature, a closed distal end, an openproximal end, and at least one region of different permeability to abone cement.

In one embodiment, the system includes a push rod adapted to beremovably insertable through the delivery device and into the expandabledevice to hold the expandable device in a collapsed configuration priorto deployment. In one embodiment, the system includes a sheath adaptedto removably extend through the delivery device and over the expandabledevice to hold the expandable device in a collapsed configuration priorto deployment.

These and other objects, along with advantages and features of thepresent invention herein disclosed, will become more apparent throughreference to the following description, the accompanying drawings, andthe claims. Furthermore, it is to be understood that the features of thevarious embodiments described herein are not mutually exclusive and canexist in various combinations and permutations.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIG. 1A is a schematic side view of a cement director and associateddeployment system prior to expansion of the cement director, inaccordance with one embodiment of the invention;

FIG. 1B is a schematic side view of the unexpanded cement director ofFIG. 1A;

FIG. 1C is a schematic side view of the cement director and associateddeployment system of FIG. 1A after expansion of the cement director, inaccordance with one embodiment of the invention;

FIG. 1D is a schematic side view of the expanded cement director of FIG.1C;

FIG. 2 is a schematic sectional end view of an example cement director,in accordance with one embodiment of the invention;

FIG. 3 is a schematic side view of a cement director attached to adeployment system, in accordance with one embodiment of the invention;

FIG. 4 is a schematic side view of the distal end of the cement directorof FIG. 3 through section A-A;

FIG. 5 is a schematic side view of the cement director of FIG. 3 exitingthrough a cannula, in accordance with one embodiment of the invention;

FIG. 6 is a schematic side view of the cement director of FIG. 3 afterexpansion, in accordance with one embodiment of the invention;

FIG. 7 is a schematic side view of the expanded cement director of FIG.6 during cement injection, in accordance with one embodiment of theinvention;

FIG. 8 is a schematic top view of the expanded cement director of FIG. 6during cement injection, placed in a vertebral body, in accordance withone embodiment of the invention;

FIG. 9 is a schematic top view of the expanded cement director of FIG. 8after cement injection, in accordance with one embodiment of theinvention;

FIG. 10 is a schematic side view of a cement director for use intreating a vertebral fracture, in accordance with one embodiment of theinvention;

FIG. 11 is a schematic side view of the expanded cement director of FIG.10 after injection of bone cement; and

FIG. 12 is a schematic side view of another cement director for use intreating a vertebral fracture, in accordance with one embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the invention relate to balloon expandable cementdirectors and at least partially self-expanding balloon expandablecement directors for insertion into a vertebral body or other bodilyarea, and related systems and methods of deployment.

An example system for delivering and deploying a cement director isshown in FIGS. 1A to 1D. In this embodiment, the system 100 includes amesh structure, e.g., a stent or cement director 105, releasably coupledto a delivery and deployment system 110. The cement director 105 may,for example, be at least partially balloon expandable with, for example,a standard angioplasty balloon catheter. The cement director 105 isshown in a collapsed form (i.e., prior to expansion) in FIGS. 1A and 1B,and in an expanded form (i.e., after expansion) in FIGS. 1C and 1D. Anexample deployment system 110 for use with the cement directorsdisclosed herein is described in U.S. patent application Ser. No.11/957,039, filed Dec. 14, 2007, the disclosure of which is incorporatedherein by reference in its entirety.

The delivery and deployment system 100 may include a distal end 150 forinsertion into a vertebral body and a proximal end 155 comprising ahandle 160, means for releasably coupling a collapsible implant to thedistal end 150 of the delivery device, and a balloon coupled at thedistal end of the delivery device and adapted to expand a collapsibleimplant, e.g., the cement director 105, when disposed therein.

In one embodiment, the cement director 105 has an outer diameter ofabout 2-4 mm and a length of about 15-25 mm when in collapsed form. Invarious embodiment, the length of the cement director 105 may be 15 mm,20 mm, or 25 mm, depending upon the size of the vertebral body intowhich it is to be placed. In an alternative embodiment, the length ofthe cement director 105 may be greater or lesser, as appropriate. Inalternative embodiments, the outer diameter, when collapsed, may begreater or lesser, depending upon the size of the vertebral body and/orthe size of the cannula through which it is inserted into the interiorof the vertebral body. The cement director 105 may be formed frommaterials including, but not limited to, metals (such as stainlesssteel), alloys (such as Ni—Ti), and/or plastics.

In one embodiment, the cement director 105 can expand by up to about400% to 500%, or more, of its collapsed diameter, depending, forexample, upon the materials used, the geometry of the cement director105, the balloon being used to expand the cement director 105, and/orthe size of the vertebral body into which it is to be placed. Forexample, in one embodiment, the cement director 105 can expand to anouter diameter of between 11 mm to 15 mm, and even up to about 17 mm. Inalternative embodiments, the cement director 105 may be adapted toexpand to a greater or lesser extent, e.g., down to about 10 mm or lessand up to about 20 mm or more. For example, various cement directors 105may be adapted to expand to between 200 and 600% of their collapseddiameter.

In one embodiment, the cement director 105 includes a closed distal end115 and an open proximal end 120, with the open proximal end 120releasably coupled to a distal end of a fill passageway of thedeployment system 110 through which, for example, a balloon can beinserted and removed, and/or cement can be injected into the interior ofthe cement director 105. The closed distal end 115 may be formed, forexample, by welding, or otherwise attaching, the distal ends of thestruts of an open stent together to seal an end of the stent. In oneembodiment, the open proximal end 120 may have a diameter ofapproximately 2-4 mm.

The cement director 105 may be covered with a covering material such as,but not limited to, a polymer. Example materials may include, or consistessentially of, silicone, polyurethane, styrene, isobutylene, polyester,nylon, natural fiber material, and/or combinations thereof. In oneembodiment, the material may be one or more textiles such as, but notlimited to, a knitted fabric, a braided fabric, and/or a woven fabric.The covering layer may cover at least one of an interior surface and anexterior surface of the cement director 105. In one embodiment, thecovering material may include, or consist essentially of, a mesh. Thismesh may, for example, be impregnated with a material such as, but notlimited to, an elastomeric polymer.

The surface of the cement director 105 may include one or more regionsof greater permeability 125. These regions of greater permeability 125may, for example, be holes created in the surface to allow a bone cementinjected into the interior of the cement director 105 to flowpreferentially out of the cement director 105 through the holes. Theholes may, for example, be arranged in a pattern along one side of thecement director 105, thereby allowing cement to flow preferentially outof one side of the cement director 105. Alternatively, the regions ofgreater permeability 125 may be regions including a more permeablematerial and/or a broader mesh.

In one embodiment, the cement director 105 may be constructed from aplurality of layers, with the regions of greater permeability 125 formedby removing one or more of the plurality of layers from one or moreregions of the surface while leaving the other layer(s) in place. Assuch, the remaining layers can provide structural integrity to thecement director even if a portion of one or more other layers is removedto produce the regions of greater permeability 125.

The regions of greater permeability 125 may be used to ensure that bonecement exits from the cement director 105 in the required direction,i.e., to appropriate areas of the vertebral body to treat a fracture orother structural failure, such as an anterior-superior and/or anteriorinferior region of a vertebral body. The regions of greater permeability125 may be of any appropriate size and shape (e.g., circular, oval,and/or square) and may be arranged in any appropriate number andconfiguration. In one embodiment, the cement director 105 may includeone or more baffled regions (as shown in FIGS. 10 and 11), with baffles280 preventing flow of bone cement through the baffled regions. Examplecement directors 105, and hole configurations therefor, are shown inU.S. patent application Ser. No. 11/957,039, filed Dec. 14, 2007, andU.S. Pat. No. 7,465,318, issued Dec. 16, 2008, which are incorporatedherein by reference in their entireties.

In one embodiment, the cement director 105 may be expanded, or partiallyexpanded, by a dilation balloon which is inserted into the interior ofthe cement director 105 either prior to, or after, insertion of thecement director 105 through a cannula and into the interior of avertebral body. The inflation balloon may, for example, be a standardangioplasty balloon that may, for example, have a folded profile of lessthan about 2 mm. In one embodiment, the cement director 105 ispositioned over the dilation balloon prior to insertion into a vertebralbody, with a total cross-sectional diameter of the cement director 105of less than about 4 mm, when in an unexpanded state. In one embodiment,the cement director 105, with the dilation balloon therein, is insertedthrough a cannula and into an interior of a vertebral body, or otherappropriate treatment site, in an undeployed configuration. The dilationballoon is then expanded (e.g., by injection of a balloon expansionmaterial such as a liquid, e.g., saline solution, through a fillpassageway in the deployment system 110) to expand the cement director105. The balloon is then withdrawn after dilatation, and cement isinjected through the delivery system 110 and into the cement director105. The cement director 105 is then detached from the delivery anddeployment system 110. Alternatively, the balloon may be inserted intothe interior of the cement director 105 after the cement director 105has been inserted into a vertebral body. Using a balloon to assist inthe expansion of the cement director 105 may be beneficial, for example,in allowing for improved controlled expansion of the cement director105, with an increased expansion force than that available through aself-expanding device to allow for reconstruction of a collapsedosteopathic vertebral body including height restoration.

The balloon may be removed from the interior of the cement director 105after expansion, but prior to cement injection. In an alternativeembodiment, the balloon may be configured to burst, or be permeable,upon full expansion, thereby allowing the cement to be injected into thecement director 105, and to escape the cement director 105 through theregions of greater permeability 125, through the same fill passageway asthe balloon expansion material, without the need to remove the balloonprior to cement injection. In a further alternative embodiment, the fillpassageway for the cement may be separate from, and exterior to, theballoon, thereby allowing the cement to be injected into the interior ofthe cement director 105 but exterior to the balloon. As a result, theballoon may be left in the cement director 105 in an unexpanded stateduring cement injection.

One embodiment of the invention includes a cement director 105 includinga multi-layered mesh structure with two or more layers. An examplemulti-layered cement director 105, as shown in FIG. 2, includes twolayers of a shape-memory material such as, but not limited to, Ni—Ti.The bi-layered cement director 105 includes an inner layer 130, formed,for example, from austenitic Ni—Ti, and an outer layer 135, formed, forexample, from martensitic Ni—Ti. In one embodiment, the transitiontemperature from martensite to austenite of the inner layer 130 is lessthan a body temperature (e.g., less than about 100° F.), and the outerlayer 135 has a transition from martensite to austenite greater than thebody temperature. The bi-layered material may, for example, befabricated into the cement director 105 shape such that the two layerscan act in combination such that they can be releasably constrained to ashape smaller that the fabricated diameter, such that the cementdirector 105 will self expand to a predetermined shape whenunconstrained and wherein the cement director 105 can be furtherenlarged by application of a force by deforming the outer martensitelayer 135 without slip deformation or “yielding” to an enlarged diametergreater than the self-expanded diameter. The cement director 105 may,optionally, include a covering layer 137.

In one embodiment, a cement director having an austenite layer may befabricated such that its original, undeformed, shape correspondssubstantially with the required final balloon-expanded shape upondelivery of the cement director into a vertebral body. The austenitelayer may then be elastically deformed to a collapsed configuration, andheld in this collapsed configuration by a sheath and/or elongate rod,during insertion and prior to deployment. As such, upon removal of thesheath and/or elongate rod, the austenite layer will deform back to itsoriginal, undeformed, shape. In one embodiment, a martensite layer maybe placed over or under, or interwoven within, the austenite layer. Inoperation, the martensite layer will try to hold its deformed shape upona deformation of the cement director into a collapsed configuration andwill, therefore, impede expansion of the austenite layer to itsoriginal, undeformed, shape. As a result, removal of the sheath and/orelongate rod will result in the cement director partially self-expanding(due to the elastic properties of the austenite layer), but notreturning fully to the original, undeformed, shape (due to themartensite layer hindering the full self-expansion of the austenitelayer). In this case, a balloon may be used to further expand thepartially expanded cement director to return it to its fully expandedconfiguration (corresponding, or substantially corresponding, to thecement director's original, undeformed, shape).

By forming a cement director from both an austenite layer and amartensite layer, and expanding the cement director within the vertebralbody to correspond in shape to the original, undeformed, shape of thecement director prior to collapsing the cement director for delivery,the cement director may provide a level of structural support for thevertebral body upon deployment, but prior to cement injection. Moreparticularly, the austenite layer of the cement director willpreferentially stay in its original, undeformed, shape, and willtherefore provide a force hindering and subsequent deformation withinthe body. In addition, the martensite layer will impede any deformationfrom its shape, and therefore provide additional force hinderingdeformation of the cement director. As such, the cement director mayprovide a certain level of structural support for the vertebral bodyeven before cement injection.

In one embodiment, a bi-layered cement director 105 may be inserted intoan interior of a vertebral body with a balloon, or other appropriateexpansion element, positioned within the interior of the cement director105. A removable sheath may be placed over the cement director 105 tohold the cement director 105 in a collapsed, undeployed, state prior toinsertion. A removable push rod may be pleased into the interior of thecement director 105 in addition to, or in place of, the sheath to assistin holding the cement director 105 in an undeployed state prior toinsertion and/or curving of the cement director to conform to the cavitythat has been created. Upon removal of the sheath and/or push rod, thebi-layered cement director 105 partially self-expands to a partiallyexpanded shape smaller than the preset shape of the austenite shapememory material. The balloon can then be used to further expand thecement director 105 to a fully expanded state (which may, for example,conform substantially to the preset shape of the austenite layer 130),with the outer martensite layer 135 assisting in holding the cementdirector 105 in its expanded state after removal of the balloon. As theouter martensite layer 135 is selected such that the transitiontemperature from martensite to austenite is greater than the bodytemperature of the patient into which the cement director 105 isinserted, the outer martensite layer 135, and therefore the cementdirector 105, will hold its shape after deformation by the balloon. Asthe material has not yielded or undergone plastic deformation duringexpansion by the balloon, the predetermined, self-expanded shape of thecement director 105 is recoverable after expansion if the temperature ofthe outer martensite layer 135 exceeds the transition temperature, frommartensite to austenite, for this material. However, as the material ofthe outer martensite layer 135 is selected such that the transitiontemperature is greater than body temperature (i.e. approximately 100°F.), this recovery will not happen during normal deployment and use.

In one embodiment, the cement director 105 is made from a shape-memoryalloy that is super-elastic/pseudo-elastic. The term super-elasticity isused to describe the property of certain alloys that can be strained intheir austenite state more than ordinary spring materials without beingplastically deformed. This unusually large elasticity in the austenitestate is called pseudoelasticity (because the mechanism isnonconventional in nature) or is called transformational superelasticitybecause it is caused by a stress induced phase transformation. Shapememory and superelasticity are particularly pronounced in Ni—Ti alloys.As a result, Ni—Ti stents created in the austenite crystal phase can bedeformed by external force without plastic deformation or yielding. Anexample vascular stent including shape memory alloys is described inU.S. Pat. No. 6,451,052 to Burmeister et al., issued on Sep. 17, 2002,the disclosure of which is being incorporated herein by reference in itsentirety. In an alternative embodiment, the cement director 105 mayinclude, or consist essentially of, a material that may self-expand to apredetermined size upon initial deployment, and thereafter plasticallydeform upon further expansion by a balloon.

In various embodiments, the multi-layered cement director 105 mayinclude any appropriate number of layers. For example, one embodiment ofthe invention may include a multi-layered cement director 105 includinga single martensitic layer or a multi-layered martensitic material. Ingeneral, as discussed above, the martensite phase material will have ahigher transition temperature than body temperature and may be pliablebut stiff depending on the thickness. While the martensitic materialretains is deformed shape after load removal (at temperatures below itstransition temperature), martensitic deformation is caused by detwinningand not through typical plastic deformation or yielding of crystal slip.In various embodiments, the cement director 105 may be a stent that isaustenite at room temperature or be entirely martensitic at roomtemperature.

In one embodiment, a cement director may be formed from a single layermesh structure formed from a first shape memory material in a martensitephase at body temperature. The cement director may include a closeddistal end, an open proximal end, and at least one region of differentpermeability to a bone cement. The martensite mesh structure isexpandable from an unexpanded configuration to an expanded configurationby expansion of a balloon within an interior of the mesh structure, andis adapted to maintain the expanded configuration after removal of theballoon from the interior of the mesh structure. By using a martensiteshape memory material, the cement director may be held in an unexpandedconfiguration without the need for a push rod and/or sheath, with thecement director being expanded to a deployed configuration throughinflation of a balloon or actuation of other appropriate expansionelement after insertion into the vertebral body.

Forming a cement director from a shape memory material in a martensitephase at body temperature may provide substantial advantages over cementdirectors formed from plastically deformable materials. For example,martensite shape memory material cement directors may provide for aratio of expansion from an unexpanded to an expanded configurationsignificantly greater than that available for plastically deformabledevices. In addition, use of martensite material may, in one embodiment,allow for overstretching of the cement director by a balloon, such thatthe cement director recoils to a predetermined diameter after removal ofthe balloon, leaving a space between the bone and the resting stentposition. In this embodiment, bone cement could then fill the void leftby the recoil of the cement director.

In one embodiment, the cement director 105 can be manufactured bycreating a tube of mesh material out of the appropriate super-elasticNi—Ti alloy. The tube may be laser cut into a stent like structure, withthe distal end thereafter sealed, for example, by welding.Alternatively, the cement director 105 may be braided into a wovenshape. In certain embodiments, a coating may be applied by dip coatingor spraying. Alternatively, a coating may be applied over the strutsover which a mesh structure is laminated to the cement director 105, anda further coating may optionally be applied to seal the mesh. Theregions of greater permeability 125 may be holes cut, for example, by ahot tip soldering iron and/or by a laser.

An example manufacturing process may include creating a bi-layer Ni—Titube, as shown in FIG. 2, or single layer of super-elastic Ni—Ti, andlaser cutting the tube into a stent like design. The stent is thenformed into a cement director 105 by putting it into a fixture androunding the ends, with the distal end 115 sealed, for example, into aball like rounded end. The cement director 105 may be covered by acovering layer 137. For example, the cement director 105 may bedip-coated, for example with silicone, an elastomeric urethane,polyurethane, isobutylene, polyester, nylon, natural fiber material,and/or a styrene rubber, to seal the openings. The cement director 105can also be covered with a nylon or polyester mesh than can be embeddedinto the elastomeric matrix and will move as the cement director 105opens, as has been done in reinforced balloons. Holes may then be cutinto the matrix covering the cement director 105 with a laser or hot tipdevice to create the regions of greater permeability 125. The unopenedcement director 105 is now ready for releasably coupling to a deliverysystem 110, as shown in FIGS. 1A-1D.

In operation, the various cement directors 105 described herein may beused to treat a fracture, or other structural failing or weakness, in avertebral body 240, as depicted in FIGS. 8-12. As discussed above, acement director 105 may be releasably coupled to a delivery system 110and inserted through a delivery cannula (i.e., a hollow channel insertedthough the skin and into the target site within the patient to allowaccess for the cement director 105). The cement director 105 may beinserted into previously created curvilinear or straight cavities orpaths created in the vertebral body 240 target site by one or moredrilling and/or reaming device as described, for example, in U.S. patentapplication Ser. No. 11/957,022, filed Dec. 14, 2007, U.S. patentapplication Ser. No. 12/486,439, filed Jun. 17, 2009, and U.S.provisional patent application Ser. No. 61/210,771, filed Mar. 23, 2009,the disclosures of all of which are being incorporated herein byreference in their entirety. An example method of inserting anddeploying the cement director 105 is shown in FIGS. 2-12.

As illustrated in FIG. 2-7, the cement director 105 may have a closeddistal end 205 and an open end 210, with the cement director 105collapsed over a hollow push rod 215 prior to inserting the cementdirector 105 into a catheter sheath 220, so that the push rod 215 iseffectively releasably linked to the closed end 205 of the cementdirector 105. (The catheter sheath may, itself, include radio opaquemarker bands 225). The proximal open end 210 is releasably coupled to adistal end of the deployment device. The hollow push rod 215 facilitatesplacement of the collapsed, enclosed mesh structure into the cavity, viaa cannula 230, through its removable connection to the closed end 205 ofthe cement director 105. The releasable connection may be a mechanicallinkage, such as a thread or luer lock, a press-fit connection, or anyother form of releasable engagement. Alternatively, the push rod may bepositioned in the cement director without being coupled to the distalend 205.

In one embodiment, during constraint of the cement director 105 in thesheath 220, the austenite layer 130 may stress induce to a martensiticstate. In the alternative, the cement director 105 may be cooled belowthe transition temperature of layer 130 to facilitate its deformationand constrainment. The martensitic layer 135 merely undergoes reversibledeformation and the cement director 105 may be loaded into the sheath220. However with temperature changes occurring up to body temperature,layer 130 will remain martensitic until the constraint is removed. Whenreleased in place in the vertebral body 240 it will expand to its selfexpanded state, e.g., about 10 mm, 15 mm, or a percentage thereof, dueto the transformation of layer 130 from martensite to austenite.

Once the cement director 105 is fully inserted into the cavity formedwithin the bone structure being treated, the sheath 220 is retracted, asillustrated in FIG. 6, and the self-restoring cement director 105expands to its final shape, as illustrated in FIGS. 6 and 7. Theself-expanding cement director 105 can self-expand to a first diameterof, for example, about 10 mm. If the physician deems it appropriate, orif the structure has not expanded fully, a balloon catheter can beinserted into the delivery system 110 through the hollow push rod 215into the interior of the cement director 105. The balloon can, forexample, be an angioplasty balloon catheter as commonly used inperipheral balloon angioplasty, and is capable of expanding to up toabout 10, 12, or even 15 mm, or greater. The balloon may then beexpended through injection of an expansion fluid, e.g., a salinesolution, under fluoroscopic guidance to achieve the distraction of theendplates shown in FIGS. 10 and 11.

The releasable connection between the closed end 205 of the cementdirector 105 and the push rod 215 (see FIG. 4) may be severed, and thehollow push rod 215 may be partially retracted until its tip is locatedgenerally in the center of the cement director 105, at which point thepush rod 215 may, in certain embodiments, be used secondarily as acement injector. In an alternative embodiment, the push rod 215 may be asolid element which removably extends through a hollow cement injectorpassageway.

A filling portal (not shown) on the other end of the rod 215 is thenconnected to a cement injection syringe via, for example, a luer lockfitting. Cement can then be injected into the center of the cementdirector 105, as indicated by the directional arrows shown in FIG. 7. Inone embodiment, the open end 210 of the cement director 105 can becollapsed around the hollow push rod 215, thereby forming a slideableconnection that assures lengthwise positioning and targeting of the flowportal of the push rod 215 within the center axis of the cement director105 and easy removal of the push rod 215 after filling with cement.

In an alternative embodiment, as shown in FIG. 8, a separate fillingneedle 250 capable of penetrating the mesh structure of the cementdirector 105 may be used to perforate the meshwork after deployment ofthe cement director 105 in the bone cavity, so that the cement injectionis not restricted to any particular vector; indeed, the cement director105 may, in various embodiments, be filled in one or more orientationsat one or more points of entry. By perforating the outer mesh, theneedle flow portal 250 may be placed in the center of the cementdirector 105 or, if necessary, entirely through the cement director 105to regions of the bone external to the cement director 105 where it maybe desirable to inject additional cement directly into a bone fracturesite.

As illustrated in FIGS. 8-12, the regions of greater permeability (e.g.,holes) 125 control the direction of flow of cement into the vertebralbody 240 into which the cement director 105 is inserted. In particularembodiments, a greater amount of cement will flow out of the holes 125as represented by the relatively thick, large arrows, than will flow outof the remainder of the cement director 105, as represented by therelatively thin, small arrows. Alternatively, the cement director 105may be configured to allow cement to flow only out of the holes 125.

For a given orientation of the cement director 105 within the vertebralbody 240, with the holes 125 facing, for example anterior-superior andanterior-inferior, significant volume of cement may be directedanterior-superior and anterior-inferior into the forward third of thevertebral body 240, thereby forming “mantles” 270 of cement which crossthe plane of the vertebral fracture 285. The cement mantles 270 may belocated adjacent to the vertebral endplates and thus will form aloadbearing column of cement, as shown, for example in FIGS. 11 and 12.By carefully directing the cement out through the holes 125 only in theappropriate direction and away from more delicate regions of thevertebral body 240, these cement mantles may be safely formed withoutendangering the patient.

In one embodiment, the cement director 105 is an at least partiallyballoon-expandable cement director made, at least in part, ofmartensitic Ni—Ti. In this case, the cement director 105 may be attachedto the hollow push rod 215 in its collapsed state. After the cementdirector 105 is inserted into the cavity formed within the bonestructure 240, a balloon, e.g., a peripheral angioplasty balloon thatmay have a profile of less than about 2-3 mm, may be inserted throughthe push rod 215 into the collapsed cement director 105. When the cementdirector 105 is fully inserted into the cavity, the balloon may beexpanded and the cement director 105 may thereby expand to its finaldeployed shape. The balloon catheter may be deflated and withdrawn fromthe push rod 215 so that cement can be injected into the cement director105 and out through the holes 125 into the vertebral body 240 at theappropriate locations.

In various embodiments, the cement director 105 may be formed to have asubstantially cylindrical shape (see, for example, FIGS. 1A-1D) or anovoid shaped form upon expansion (see, for example, FIGS. 6-9). Inalternative embodiments, other shapes may be desirable for the expandedcement director 105 shape. For example, an oblong or pear-shaped cementdirector 105 might be desired when, for example, it is clinicallydesirable or necessary to approach the vertebral body 240 bilaterally,through each pedicle, as illustrated, for example, in FIG. 12.Alternatively, a relatively thin cement-directing structure may beemployed for spinal fusion techniques, wherein the cement-directingstructure is deployed through minimally invasive means into the discspace to provide support to the spinal column following discectomy. Incertain embodiments, the cement director 105 may be formed to follow acurvilinear pathway formed in a vertebral body, upon expansion.

In addition, various embodiments of the invention may include a cementdirector 105 formed from a braided mesh structure. In alternativeembodiments, self-expanding, collapsible mesh structures can be formedby a variety of other techniques including, but not limited to,laser-cutting tubes.

It should be understood that alternative embodiments, and/or materialsused in the construction of embodiments, or alternative embodiments, areapplicable to all other embodiments described herein.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The foregoingembodiments, therefore, are to be considered in all respectsillustrative rather than limiting the invention described herein. Scopeof the invention is thus indicated by the appended claims, rather thanby the foregoing description, and all changes that come within themeaning and range of equivalency of the claims are intended to beembraced therein.

What is claimed is:
 1. A system for treating a vertebral bodycomprising: a delivery device comprising a distal end configured forinsertion into a vertebral body and a proximal end comprising a handle;an expandable device configured to be releasably coupled to the distalend of the delivery device, the expandable device comprising a meshstructure comprising a plurality of layers including a first layercomprising a first shape memory material in an austenite phase at bodytemperature and a second layer comprising a second shape memory materialin a martensite phase at body temperature, wherein by forming the meshstructure with the austenite layer and a martensite layer, the meshstructure is configured to correspond in shape to an original undeformedshape of the mesh structure prior to collapsing the mesh structure fordelivery, the mesh structure provides structural support for thevertebral body upon deployment and prior to cement injection, and aballoon configured to be coupled at the distal end of the deliverydevice and adapted to expand the expandable device when disposedtherein.
 2. The system of claim 1 further comprising a push rod adaptedto be removably insertable through the delivery device and into theexpandable device to hold the expandable device in a collapsedconfiguration prior to deployment.
 3. The system of claim 1 furthercomprising a sheath adapted to removably extend through the deliverydevice and over the expandable device to hold the expandable device in acollapsed configuration prior to deployment.
 4. The system of claim 1,wherein the mesh structure is generally cylindrical in shape, whenexpanded, such that an outer diameter along at least a portion of alength of the mesh structure is substantially constant.
 5. The system ofclaim 1, wherein the mesh structure includes at least one region ofgreater permeability relative to a second region of lesser permeability.6. The system of claim 5, wherein the region of greater permeabilityincludes a plurality of holes positioned along a length of the meshstructure.
 7. The system of claim 1, wherein the mesh structure furtherincludes a covering layer.
 8. The system of claim 7, wherein the meshstructure includes at least one region of greater permeability relativeto a second region of lesser permeability, and the region of greaterpermeability comprises a region that is not covered by the coveringlayer.
 9. The system of claim 7, wherein the covering layer isimpermeable to bone cement.
 10. The system of claim 7, wherein thecovering layer comprises an elastic material.
 11. The system of claim10, wherein the elastic material is selected from the group consistingof silicone, polyurethane, styrene, isobutylene, polyester, nylon,natural fiber material, and combinations thereof.
 12. The system ofclaim 1, wherein at least one of the first and second shape memorymaterials comprises nickel titanium.
 13. The system of claim 1, whereinthe expandable device includes a closed distal end and an open proximalend.
 14. The system of claim 13, wherein the delivery devices includes afill passageway, and wherein the open proximal end of the expandabledevice is configured to be releasably coupled to a distal end of thefill passageway in the delivery device.
 15. The system of claim 1further comprising at least one of a drilling device and a reamingdevice configured to form a path and/or a cavity in the vertebral body.16. A system for treating a vertebral body comprising: a delivery devicecomprising a distal end configured for insertion into a vertebral bodyand a proximal end comprising a handle; an expandable device configuredto be releasably coupled to the distal end of the delivery device, theexpandable device comprising a mesh structure comprising a plurality oflayers including a first layer comprising a first shape memory materialin an austenite phase at body temperature and a second layer comprisinga second shape memory material in a martensite phase at bodytemperature, wherein the mesh structure includes at least one region ofgreater permeability relative to a second region of lesser permeability,and a balloon configured to be coupled at the distal end of the deliverydevice and adapted to expand the expandable device when disposedtherein.
 17. The system of claim 16, wherein the region of greaterpermeability includes a plurality of holes positioned along a length ofthe mesh structure.
 18. The system of claim 16, wherein the expandabledevice is collapsible to a collapsed state and expandable to an expandedstate by inflating the balloon within the expandable device.
 19. Thesystem of claim 16 further comprising a push rod adapted to be removablyinsertable through the delivery device and into the expandable device tohold the expandable device in a collapsed configuration prior todeployment.
 20. The system of claim 16 further comprising a sheathadapted to removably extend through the delivery device and over theexpandable device to hold the expandable device in a collapsedconfiguration prior to deployment.